Biosensing platforms using graphene based bioreactive nanostructures with various dimensions

Sammanfattning: Nanomaterials have brought new aspects and improvements to the biosensing field due to their unique physical and chemical properties that are not shown in the bulk state. This thesis focuses on concepting, developing and testing of biosensors where nanomaterials including graphene gold nanoparticles (AuNPs) and magnetic nanoparticles (MNPs) constitute the biosensors. The motivation is to improve the properties of biosensors for protein and nucleic acids by using the nanomaterials’ high surface volume ratio, their unique electrical properties, their good stability and biocompatibility.The synthesis of well controlled hybrid materials was essential to obtain well performing nucleic acids sensors, whereas a protein sensor contained mainly graphene and organic molecules. The nanomechanical measurements were applied on pyrene-maltose functionalized graphene surfaces after incubating them with the protein. When the Concanavalin A was captured by the pyrene-maltose, the adhesion force of biosensor surface increased significantly. This detection principle was employed to quantify the Concanavalin A attachment to the surface sensitively.In the development of the eletrocatalytic microRNA sensor, AuNPs were packaged into graphene oxide (GO) sheets to form three-dimensional network structures that both guide the electrical current and increase the surface area of the electrodes. Prior to the assembly of these GO-AuNPs hybrid materials, a duplex-specific nuclease-assisted target recycling reaction was employed for opening the surface of the DNA functionalized AuNPs. The electrocatalytical water splitting activity increased with the fraction of the AuNP surface and thus with the activity of the nuclease-assisted target recycling reaction.Owing to the high shape anisotropy of graphene, a two-dimensional optomagnetic label GO-MNP nanohybrid was investigated for DNA detection. The DNA coils that were generated through rolling circle amplification absorbed on GO-MNP nanohybrid, leading to a hydrodynamic size increase or aggregation of the proposed nanolabels that can be detected by an optomagnetic sensor. An MNP assembly-based microRNA biosensing strategy is also included in the thesis. DNA scaffolds of the MNP assemblies contain DNAzyme substrate and thus can form cleavage catalytic structures in the presence of microRNA, leading to the disintegration of assemblies. The proposed nanomaterials based biosensing platforms show great potential in the clinical and biomedical applications.